<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    * {
      box-sizing: border-box;
    }
    body {
      margin: 0;
    }
    .container {
      width: 100%;
      /* margin: 0 auto; */
      margin-left: auto;
      margin-right: auto;
    }
    .item {
      width: 100%;
      padding: 15px;
      float: left;
    }
    .content {
      width: 100%;
      height: 200px;
      background: #000;
      margin-bottom: 20px;
    }
    
    @media (min-width: 768px) {
      .container {
        width: 750px;
      }
      .item {
        width: 100%;
      }
    }
    @media (min-width: 992px) {
      .container {
        width: 970px;
      }
      .item {
        width: 50%;
      }
      
    }
    @media (min-width: 1200px) {
      .container {
        width: 1170px;
      }
      .item {
        width: 50%;
      }
    }


    
  </style>
</head>
<body>
  <!-- 
    > 1200  1170
    > 992  970
    > 768  750
    < 768  100%
   -->
  <div class="container">
    <div class="item">
      <div class="content"></div>
    </div>
    <div class="item">
      <div class="content"></div>
    </div>
    <div class="item">
      <div class="content"></div>
    </div>
    <div class="item">
      <div class="content"></div>
    </div>
  </div>
</body>
</html>